Method for the smelting of iron ores



United States Patent '0 METHOD FOR THE SMELTING OF IRON ORES Ingvald A. Kjellman, Abo, Finland Application March 10, 1953, Serial N0. 341,419

4 Claims. or. 75-41 For making pig iron using a basic slag it is generally necessary to add a slagging material to the iron ores and the coke, which together with the gangue of the ore and the ash of the coke will form a slag which, with out being too viscous at the temperature prevailing at the hearth of the blast furnace, is basic enough for absorbing most of the sulphur entering with the stock. Because the gangue of the ores and the ash of the coke normally are acid, the slagging material mainly consists of basic minerals, chiefly limestone.

During the descending of the stock down the shaft, it is being heated. Simultaneously herewith a reduction of the oxides in the ore through the ascending reducing gases is started at the top of the shaft. As the gangue of the ore and the ash 'of the coke do'not react with the limestone added until the temperature is high enough, the slag forming reactions do not take place until in a later phase, due to the well known fact that reactions between solid phases are very slow. Therefore the slag reactions mainly take place in the lowest part of the blast furnace. The time during which the final slag can react will consequently become so short, that desired reactions cannot be concluded as far as required.

It is earlier known to add finely ground limestone to the iron ore concentrates before sinten'ng in order to obtain a self fiuxing sinter. Hereby a certain amount of calcium silicate is formed already during the sintering process.

' It has also been proposed, for the mentioned purpose, simultaneously to add returned blast furnace slag. A resulting phenomenon of these steps is that the limestone and the slag have reacted with the ore at a somewhat more favourable phase, but nevertheless it has not been possible by known methods to obtain a fully satisfactory desulphurization, manganese recovery and carbon content in pig iron.

very early stage and it will also be accelerated with the efiect that the reduction is concluded at an earlier stage than in known process, resulting in a final slag with a lower oxygen pressure. As a consequence of the low oxygen pressure follows that the ratio able and also that the carbon content of the pig iron will be high.

The capacity of sulphur absorption of an otherwise given basic Slag is, however, quite decisively also depending upon the oxygen pressure, provided the Fe()- content is low, which is the case with basic blast furnace slags (see: Chipman; Metal Progress, December 1952).

"This is obtained by the present invention which relates to a method founded on an entirely new principle.

According to the present invention a low sulphur content of the pig iron, a good manganese recovery in the blast furnace and a high carbon content in the pig iron is obtained without connecting the process with any steps for producing a self fluxing sinter. According to this new and improved method a sinter is made, the slagging components of which, though containing basic components, are considerably more acid than an ordinary blast furnace slag. The basicity required for desulphurization will be attained in a later phase of the smelting process, when limestone in lumps added to the stock will react with the slag at a high temperature. The primary acid slag formed in the sinter is easily fusible and highly reactive, and will absorb large amounts of iron oxides from the sinter, with which it lies in close contact. The iron content of the slag, however, will quickly be reduced, due to the close contact with the coke and the reducing atmosphere, whereafter the acid slag again can react with new quantities of iron oxide. In this way the reduction process in the blast furnace will start at a The low oxygen pressure of the final slag will also cause an increase of the ratio A i. e. the sulphur content in the slag increase in proportion of the sulphur content in the pig iron, incomparison with known methods. Consequently, the sulphur content of the pig iron will be exceptionally low, provided the quantity of the slag and the basicity of the final slag is normal.

These mentioned advantages have been obtained by bringing the iron ore, before its charging into the blast furnace, into close contact with a slagging material with specific qualities. The composition and quantity of this material is according to the invention determined with regard to the gangue of the iron ore, whereas the composition of the final slag is adjusted by adding basic slag forming material to the burden.

The addition of the first mentioned slagging material adapted to react at an early stage with the gangue of the ore and with the iron oxides will most conveniently be effected in connection with the transformation of the iron ore concentrate into lumps by a method such as sintering, pelletizing, agglomeration etc. The slagging material may conveniently be added as finely ground and consists partly or entirelyof ready produced silicates, for inst. metallurgical slags. Even if these slags as well as the coke fines used for the sintering, contain some per cent of sulphur, a sinter with low sulphur content can easily be produced by keeping the grain size. of the raw materials3 mm.

The composition of the slagging material should be selected so as to give the product from the reaction with the gangue of the iron ore a fairly low melting point and further so that it will become more acid than the desired final slag, giving it a sufficient capacity for dissolving FeO. According to the invention, the product from the reaction should as far as the most important components, SiOz, A1203 and CaO are concerned, lie within the dotted region ABC-DE-F in the ternary diagram CaO-iOz-AlzOs shown in the accompanying drawing. Said region is comprised within an area bordered by the percentage lines corresponding to 5% and 25% for A1203, 40% and 66% for Bio: and 18% and 46% for CaO.

In the diagram the region for basic blast furnace slags has also been indicated below the aforementioned region in the drawing.

The percentage of other slagging components such as MgO, alkalies, TiOz, should be kept at their normal values.

It is evident that the purpose of the invention is to obtain a better desulphurization, better manganese recovery and a higher carbon content in the pig iron, with normal basicity of the final blast furnace slag, in connection with the charging of the furnace distributing the necessary slagging components in a special way. It

should also especially be observed that by running the blast furnace according to the invention the basicity of thefinal slag can be increased,'without complicating the.

Said severe drawback is avoided by the present invention according to which the iron oxides are dissolved inga more acid slag the quality of which being such that the melting point .and viscosity are decreasing with the advancing reduction of the iron. The highly basic final slag is not being formed until at a later phase when the iron reduction is far advanced and when there is less danger for a lime set. Consequently a more basic final slag can be used according to the present improved method.

As an example of results obtained in practice by this method, the following data may be given.

(1) Starting with typically acid iron ore concentrates to which were added suitable slagging materials, a sinter with the following analysis was produced:

Percent SiO 8.58 A1 2.84

CaO 5.19

MgO= 1.09 Fe =57.34

This composition is indicated on the attached CaO-SiO2AlzO3-diagram, point P.

At the smelting process was a coke containing 1.12% sulphur used.

' (2) The composition of the final blast furnace slag, the quantity of which was 400 kgs/ton pig iron, was as follows:

Percent SiO =29.92 AlgO3=1-5.09 CaO =46.63

Mg0= 6.71 MnO= 0.21

(3) Analysis of pig iron obtained wast Percent C =4.43 Mn=0.84-

From the above the following facts may be calculated:

Sulphur content of the slag (S) 3.05 Sulphur content of the pig iron {S1 0.008

Manganese quantity in the pig iron Manganese quantity in the slag 0844000400129 8.4 kg. -021-400 0.65 kg.

correspondingto a manganese recovery of I It has been possible to keep the sulphur content in" continuous operation below 0.006% and in some cases to bring it down as low as to 0.003%.

What I claim is: 1

1. A process for smelting iron ore for the formation of low sulphur, high carbon pig iron within the blast furnace, which pig iron requires no further desulphurization outside of said furnace comprising, mixing and bl'i', quetting, finely divided iron ore and acid slag, the latter consisting of CaO, A: and SiOz within the composition delimited by the closed'area of the ternary diagram of the figure of thedrawing whereby the mixture fuses and reacts to absorb large amounts of iron oxides in the said slag, said iron oxides which are absorbed by said acid slag being readily transformable into low .sulphur pig iron by treatment with coke and. limestone at the lower and hotter portion of said furnace to produce a by-product basic slag effectively retaining substantially all of the sulphur contained in said ore and providing for a high carbon content and high manganese recovery in the iron pigs after reduction with coke and limestone. 7

2. A process for smelting iron ore for the formation of low sulphur, high carbon pig iron within the blast furnace, which pig iron requires no further desulphurization outside of said furnace, comprising, mixing and briquetting finely divided iron ore and acid slag, the latter consisting of CaO, A120; and .SiOz within the composition delimited by the closed area of the ternary diagram of the figure of the drawing whereby the mixture fuses and reacts to absorb large amounts of iron oxides in the said slag, reducing said so-treated acid slag in the lower part of said furnace with coke and sufiicient limestone to form a basic slag, said basic slag effectively retaining substantially all of the sulphur contained in said ore and providing for a high carbon content and high manganese recovery in the iron pigs after reduction with coke and limestone. V

3. A method as in claim 1 wherein said acid slag is metallurgical slag. V I

4. A method as in claim 2 wherein said acid slag is metallurgical slag.

References Cited in the tile of this patent UNITED STATES PATENTS Etter Dec. l9, 1899 Faust June- 14, 1938 

1. A PROCESS FOR SMELTING IRON ORE FOR THE FORMATION OF LOW SULPHUR, HIGH CARBON PIG IRON WITHIN THE BLAST FURNACE, WHICH PIG IRON REQUIRES NO FURTHER DESULPHURIZATION OUTSIDE OF SAID FURNACE COMPRISING, MIXING AND BRIQUETTING FINELY DIVIDED IRON ORE AND ACID SLAG, THE LATTER CONSISTING OF CAO, A12O3 AND SIO2 WITHIN THE COMPOSITION DELIMITED BY THE CLOSED AREA OF THE TERNARY DIAGRAM OF THE FIGURE OF THE DRAWING WHEREBY THE MIXTURE FUSES AND REACTS TO ABSORB LARGE AMOUNTS OF IRON OXIDES IN THE SAID SLAG, SAID IRON OXIDES WHICH ARE ABSORBED BY SAID ACID SLAG BEING READILY TRANSFORMABLE INTO LOW SULPHUR PIG IRON BY TREATMENT WITH COKE AND LIMESTONE AT THE LOWER AND HOTTER PORTION OF SAID FURNACE TO PRODUCE A BY-PRODUCT BASIC SLAG EFFECTIVELY RETAINING SUBSTANTIALLY ALL OF THE SULPHUR CONTAINED IN SAID ORE AND PROVIDING FOR A HIGH CARBON CONTENT AND HIGH MANGANESE RECOVERY IN THE IRON PIGS AFTER REDUCTION WITH COKE AND LIMESTONE. 